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alchemy

I used to work as an alchemist.

No really. It was probably the coolest job I ever had, though technically it was called “fire assay” and not alchemy. But it has clearly alchemical origins since it apparently turns lead into gold. It doesn’t really, of course, but when it was discovered it sure must have seemed like it.

What it really does is extract platinum group metals (and silver, as it turns out) from a mixture. In our case the mixture was a “flux” of borax, lead oxide, silica, and flour; and a powdered rock sample. What happens is, the whole thing cooks down, the platinum group metals in the rock sample bond to the lead, and then you separate the lead from the other metals. Measure the recovered metal and compare with the mass of the original rock sample and you have the proportion of gold in the sample. It’s a great technique for surveying very large areas and looking for regional spikes of relatively low value, indicating a possible gold source underground.

The steps are great fun. Easily the most butch job I had.

Crucible. Or, as it is in the filename on my desktop, “curcible”. Apropos.

It doesn’t start that way. It starts more like cooking — take a pre-measured volume of flux in a ceramic crucible and add the powdered pre-measured sample. In my case this was just 10 grams since we were doing very broad survey stuff. Then test the sample with a drop of nitric acid. Does it smoke? Then it’s a carbonaceous rock and you want to add a little extra silica. No smoke? Silicaceous, maybe add a little borax. Then add a measure of flour. Flour is the critical reagent because it’s the source of carbon that will make the whole process work. Too much flour and you’ll draw out too much metallic lead. Too little and you get no lead. You want a very consistent amount of lead. So if you have carbonaceous rock, add a little less flour. If you have a soil sample (always a nightmare), no flour at all is probably best. Finally, plop in a very precise and tiny amount of silver nitrate.

Row upon row of very fucking hot.

Next you put your crucible in a 1500ºC furnace. In fact you put 24 in at once — this is a production line process! Let that cook for 40 minutes or so. While it’s cooking, the carbon will bond with oxygen in the lead oxide producing metallic lead. This lead will alloy with all platinum group metals (and the silver) in the mixture. So when it’s done you have a crucible full of molten glass and borax and a little slug of molten lead at the bottom.

Mmmm, muffins.

Now you pour these out into an iron muffin tin. Seriously, it looks exactly like a muffin tin except the cavities are conical — pointed at the bottom. Let it cool and you have a bunch of glass muffins with lead tips. And then the fun begins.

When they are solid but still very hot, you put the muffin tin by your smashing station which has protective goggles, an anvil, and walls to keep everyone but you safe. You bang on one of the muffins with your cold ball peen hammer and it fractures from the temperature differential. Scoop out the lead divot with your giant tweezers and bang it into a cube on the anvil. This is mostly to get all the glass out of the sample. Now you have a lot of shattered glass and 24 little lead cubes that are allowed with valuable other metals.

A cube of lead! Now how do you turn it into gold?

Cute little poisonous cups.

You put each lead button on a porous ceramic cupel, a little cup with a very thick base. Then those go back in the furnace but — critically — with the vent open. As the lead melts it oxidizes away thanks to the air from the vent, disappearing up the reclamation system and hopefully not into the atmosphere. But the platinum group metals do not oxidize and the silver won’t oxidize much (and you’re not measuring it anyway). After a few hours your cupels are yellow-orange from absorbing all the lead oxide and each contains a little bead of silver — the silver from the silver nitrate you put in at the beginning. Also gold and platinum but mostly silver — you put the silver in in the first place so you get something practical to analyze since the volume of gold is usually very very tiny.

See that little bead? That’s not even the gold. That’s the drop of silver you put in at the beginning. Once I saw actual gold in there and the geologist was arrested shortly thereafter for spiking his samples.

Then you give these to a real chemist who dissolves them in acid and fires them through a spectrometer of some kind to get the final results.